Communications network equipment and apparatuses (transmitters and receivers) generally implement the OSI (Open Systems Interconnection) model proposed by the ISO (International Standards Organization) which describes the functions needed for communications between two entities of a computer network and the organization of these functions, distributed according to a layered structure, the lowest layer being the “physical” level layer (called the “physical layer”) in charge of the effective sending and receiving of the signals. These different functions are generally implemented by specific components of the communications entities.
The physical layer interfaces with the immediately higher layer (data link layer) which manages communications between two adjacent machines, directly interconnected by a physical support through the MAC (“Medium Access Control”) sub-layer.
In the OSI model, each layer has a well defined role for communications between the entities of a communications network, and each role is generally implemented by one or more components adapted to this purpose. In particular, the physical-layer/MAC-layer structure of current systems is perfectly partitioned.
The physical layer defines techniques aimed at ensuring the transmission of data at a fixed bit rate. It has no knowledge, as such, of the data transported.
The MAC layer defines techniques aimed at organizing the transmission of data from the different users, managing access to the channel, collisions, acknowledgments and retransmissions, and identifying the communications entities (the terminals in particular).
Thus, the role of the MAC layer is especially that of filtering the frames received in keeping only those intended for it, in verifying their destination MAC address.
Energy-saving modes known as “power save” modes have been defined, especially by the 802.11 standards of the IEEE (Institute of Electrical and Electronics Engineers), which guarantee interoperability between wireless communications apparatuses and especially between Wi-Fi (Wireless Fidelity) type wireless communications entities.
There are different energy-saving modes. For example, one mode, called the “legacy power save” mode is based on the exchange of signaling messages (PS-Poll), sent with low modulations and without priority. An energy savings mode of this kind is therefore unsuited to real-time traffic.
There also exists a mode known as the APSD (“Automatic Power Save Delivery”) introduced into the 802.11e standard and better adapted to VOIP (“Voice Over Internet Protocol”) type traffic in which the data frame is sent with a priority relative to the type of traffic, without the presence of a supplementary management frame.
Finally, the mode known as the “PSMP” (Power Save MultiPoll) mode, introduced with the 802.11n standard, stipulates that an access point will carry out the scheduling of the periods of activity and standby of each communications entity (terminal) associated with the BSS (“Basic Service Set” designating a set of synchronized communications entities).
The access point informs an entity when traffic is intended for it. When the entity is in “active” mode, it can be in one of three states: “Standby”, “Reception” or “Transmission”.
The idea behind these different mechanisms is that of creating energy-saving modes for the mobile reception entities in alternating between standby phases (when energy is saved) and phases of activity. The different protocols and techniques cited define the exchanges between entities and access point to manage these different phases without losing any packets: they provide for a buffer storage of the packets during the standby phase and a transmission or reception of the packets during the phase of activity.
In all these prior-art mechanisms, the placing of an entity on standby is commanded at the MAC layer, which controls the energy-saving mechanism, or at the level of the higher layers. Indeed, the information exchanges between an access point and an entity are understood and analyzed only from the MAC layer onwards. It is therefore from this layer that it is possible to control the placing of the entity on standby and its activation.